Plant Colonization of Land Notes

How Plants Colonized Land

Relationship to Charophytes

Land plants are closely related to charophytes. Evidence includes:

• Rings of cellulose-synthesizing proteins.
• Structure of flagellated sperm.
• Formation of a phragmoplast.
• Comparisons of nuclear, chloroplast, and mitochondrial DNA.

Living on Land: Benefits and Disadvantages

Benefits:

• Sunlight.
• CO2.
• Soil rich in nutrients.

Disadvantages:

• Desiccation.
• Lack of support.

Adaptations to Terrestrial Life

Derived Traits (5 Key Traits)

• Alternation of generations.
• Multicellular, dependent embryos.
• Walled spores produced in sporangia.
• Multicellular gametangia.
• Apical meristems.

Other Adaptations

1. Adaptations to withstand desiccation (cuticle and closing of stomata).
2. Adaptations to move water from roots to tips of the plant body (water-conducting xylem tubes and food-conducting phloem tubes).
3. Adaptations to growing upright (dead xylem tubes provided support).
4. Adaptations for reproduction on land (live near water, use rainwater, use pollinating agents).

Key Terms

• Alternation of generations: A life cycle where a sporophyte generation alternates with a gametophyte generation.
• Sporophyte: A $2n$ spore-producing body.
• Sporangia: Structures on the sporophyte in which $n$ spores are produced.
• Microspores: $n$ male spores.
• Megaspores: $n$ female spores.
• Gametophyte: An $n$ gamete-producing body.
• Gametangia: Structures on the gametophyte in which $n$ gametes are produced.
• Archegonia: Female gametangia.
• Antheridia: Male gametangia.

Haplodiplontic Life Cycle

Involves both a haploid ($n$) gametophyte and a diploid ($2n$) sporophyte generation.

• Gametophyte (n) produces gametes (n) via mitosis.
• Gametes fuse during fertilization to form a zygote (2n).
• Zygote develops into a sporophyte (2n) via mitosis.
• Sporophyte produces spores (n) via meiosis.
• Spores develop into gametophytes (n) via mitosis.

Plant Groups

Bryophytes

(Liverworts, Mosses, Hornworts)

• Non-vascular tissue.
• No true roots, stems, leaves.
• Dominant gametophyte.
• Require water for reproduction

Liverworts (Phylum Hepatophyta)

• Gametophyte conspicuous; sporophyte dependent on gametophyte.
• No stomata.
• Plant body is a thallus.
• Asexual reproduction via gemma.
• Have rhizoids, but no true leaves, stems, or roots.

Mosses (Phylum Bryophyta)

• Gametophyte conspicuous; sporophyte dependent on gametophyte.
• Stomata on sporophyte, yet dependent on gametophyte.
• Have rhizoids, but no true leaves or stems.
• Erect gametophyte

Hornworts (Phylum Anthocerophyta)

• Gametophyte conspicuous; sporophyte dependent on gametophyte (minimal dependence).
• Stomata on sporophyte.
• Photosynthetic sporophyte.
• Flattened gametophyte.
• Have rhizoids, but no true leaves or stems.

Tracheophytes

(Lycophytes and Ferns)

• Vascular tissue.
• True roots, stems, leaves.
• Dominant sporophyte.

Lycophytes (Phylum Lycophyta)

(Club mosses, spikemosses, quillworts)

• Have lycophylls.
• Vascular system.

Monilophytes (Phylum Monilophyta)

(Ferns, Horsetails, Whisk ferns)

Whisk Ferns

• Sporophyte dominant.
• No roots or leaves.
• Rhizome for support.
• Mycorrhizal association with fungi.
• Evenly branched stems.
• Sporangia at tips of stems.
• Asexual reproduction from rhizome.

Horsetails

• Sporophyte dominant.
• Roots and non-photosynthetic leaves present.
• Underground rhizome present.
• Sporangia aggregated at tips of stems called strobili.
• Asexual reproduction from rhizome.

Ferns

• Sporophyte conspicuous.
• Roots and leaves present.
• Rhizome present.
• Sporangia clustered on the underside of leaves (sori).

Plant Phylogeny

• Green algae (Charophytes) are the ancestors of land plants.
• Bryophytes are the non-vascular plants (liverworts, mosses, hornworts).
• Tracheophytes are the vascular plants. Seedless vascular plants (Lycophytes (club moss) and Monilophytes (ferns)).
• Seed plants: Gymnosperms and Angiosperms.

Table 29.1: Ten Phyla of Extant Plants